I seem to have very similar issues. Using a Lenovo ThinkPad X1 Carbon 7th gen and ThinkPad USB-C Dock Gen 2. But I also see this on a different docking station. I'm pretty sure they are both using USB-C DP- alt mode.
When I boot my laptop connected to the docking stations, I can see BIOS POST messages, but the moment it switches to my LUKS encryption prompt the display turns off. It is visible on the laptop screen. I don't think I see any relevant kernel messages in dmesg. This does not happen to me on 5.8.0-7642-generic (this is a Pop!OS specific kernel, but don't think that matters). I've also tested 5.11.0-25-generic, and the issues persists. This RedHat bug report seems very similar: https://bugzilla.redhat.com/show_bug.cgi?id=1879442 Which links to: https://gitlab.freedesktop.org/drm/intel/-/issues/2579 The DRM error "DPCD read on addr 0x60 for 1 bytes NAKed" was also reported there. And resolved with backports of the drm code to 5.11. Could this bug report be the same problem? ** Bug watch added: Red Hat Bugzilla #1879442 https://bugzilla.redhat.com/show_bug.cgi?id=1879442 ** Bug watch added: gitlab.freedesktop.org/drm/intel/-/issues #2579 https://gitlab.freedesktop.org/drm/intel/-/issues/2579 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1908139 Title: ThinkPad T14s external display not working on ThinkPad USB-C Dock Gen2 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1908139/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
